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Pregnancy bleeding in your third trimester

Help and advice on what to do if you start to bleed during your third trimester of pregnancy

Antepartum haemorrhage (APH) is defined as any vaginal bleeding after the 28th week of pregnancy. Even if the bleeding is intermittent and painless it is essential that it is fully investigated. Above all don't panic and remember that 35% of cases relate to minor conditions such as cervical ectropion and cervical polyp, and in another 40%, no specific cause is found.

APH occurs in around 3% of pregnancies and about a quarter of these relate to one of two potentially serious conditions, placenta praevia and placental abruption. All cases of APH require hospital admission for investigation, as both placenta praevia and placental abruption can put mother and baby at risk.

What is placenta praevia?

This term describes a placenta which is lying low in the uterus (womb). In the most serious cases of placenta praevia, the lower edge of the placenta may partially or even completely cover the inner rim of the cervix. In minor cases, the lower edge of the placenta is low lying but at worst only reaches the edge of the cervix. Placenta praevia usually leads to recurrent painless bleeds from around 32 weeks onwards. It occurs in about 1 in 200 pregnancies, and is more common with twin pregnancies, increasing maternal age and previous caesarean section. The diagnosis is made by ultrasound scan.

Usually, the bleeding settles whilst the patient is in hospital. If the degree of placenta praevia is severe, the woman may have to stay in hospital for the remainder of the pregnancy as the risk of severe haemorrhage is significant. In this situation, delivery is by elective Caesarean section, as the risk to mother and baby from vaginal delivery are considerable.

With more minor degrees of placenta praevia, close out-patient monitoring is undertaken, and labour is induced.

What is placental abruption?

This term describes separation of the placenta from the wall of the uterus. This can be very sudden and severe, and leads to bleeding into the space between the separated placenta and the uterine wall. It can be life threatening for both mother and baby.

Typically, the woman has sudden, severe abdominal pain, usually associated with some dark red vaginal bleeding or clots. Occasionally the internal haemorrhage is only associated with a small amount of vaginal bleeding, but the total blood loss can be considerable with little outward sign of bleeding. Placental abruption is an obstetric emergency, and immediate hospital admission is required. The mother may become shocked due to blood loss, and the foetus may die. In severe cases, the baby is delivered by emergency caesarean section.

In more minor cases of placental abruption, hospital admission and strict bed rest are all that is required to stop the bleeding. If the bleeding doesn't recur, the woman is allowed home and the pregnancy is closely monitored thereafter.

What about the 40% with unknown cause?

There are several theories about possible underlying reasons, including bleeding from small vessels in the amniotic membranes, and bleeding from the edge of a normal placenta.

Although most cases of APH don't have a serious underlying cause, any vaginal bleeding after 28 weeks of pregnancy should be reported immediately to your midwife or GP. All women should be admitted to hospital, and it is vitally important that a vaginal examination is not performed prior to hospital admission.